Much of the buzz in the defense community tends to focus on the Air
Force with major aircraft programs like the F-35 and the ongoing tanker debacle. Other
branches of the military are also working in some very interesting projects for
new weapon systems.

The Navy announced last week that it hit a milestone with its railgun project. The
railgun fires a very fast projectile that is accelerated with electricity
rather than gunpowder or explosives. The weapon payload uses kinetic energy to
destroy targets rather than a high-explosive warhead.

The Navy milestone hit last week was the world-record 33-megajoul shot
from the electromagnetic Railgun aboard the Navy Surface Center Dahlgren
Division. A megajoule is a measurement of energy associated with a mass
traveling at a certain velocity. A one-ton vehicle moving at 100mph is a single
megajoule of energy.

"Today's railgun test demonstrates the tactical relevance of this
technology, which could one day complement traditional surface ship combat
systems," said Rear Adm. Nevin Carr, chief of naval research.

The 33-megajole shot is capable of reaching targets at extended ranges
with a velocity in the area of mach five. The Navy says that the rail gun has
many benefits other than the ability to shoot projectiles over one hundred
miles with accuracy. The electromagnetic weapon improves safety on the ship because
there are no traditional propellants needed and the projectiles need no
high-energy explosive warheads.

"The
33-megajoule shot means the Navy can fire projectiles at least 110 nautical
miles, placing Sailors and Marines at a safe standoff distance and out of
harm's way, and the high velocities achievable are tactically relevant for air
and missile defense," Rear Admiral Carr said. "This demonstration
moves us one day closer to getting this advanced capability to sea."

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Last I heard of this technology I dont believe they shoot explosive rounds but round circular tubes that the velocity alone destroys the target. Potentially on the plus side we dont have unexploded munitions lying around.

For the record land mines scare the heck out of me. I cant imagine living in a country where there are known to be tons of them still around.

You need to find the person who told you you'll be seeing a multi-megajoule rail gun on a tank any time soon and make sure they're in the seat beside you in Phys 101 next semester. These projects make sense for large warships since many are nuclear powered and have the ability to generate the kind of energy and space you need for these weapons, and even then they won't be in active service soon.

I don't know what the 'size' requirements are for this gun are, but the power requirements are a mere 9KW/hrs per shot. So the energy of the shot requires about $1 worth of electricity. The batteries in current electric cars would be able to fire a several rounds each. I would be curious how efficient these devices are though.

These rail guns are huge, and the power requirements are more than you would think. You're talking energy, which isn't the same as power. You can't use a battery, other than for storage as you can't draw energy from it quickly enough. You need a capacitor bank, and the energy density of even good capacitors is lower than that of batteries. A big capacitor bank is BIG, even if you get energy density of 0.05MJ/L (very good for a capacitor) to store 50MJ you'd be looking at 1000L (1 cubic meter) even outside of all the packaging and external circuitry you'd need. As far as efficiency, I'm not sure, but a previous 10MJ test used a 9MJ+33MJ capacitor bank.

If you want to assume 33% efficiency, for a 10MJ gun you'd need 33MJ of capacitor storage, maybe a large battery system to provide extra storage, and a generator large enough to power it. The M1A1 can do 10 rounds per minute, even doing 1 round a minute constant with battery enhancement for burst firing would require about half a megawatt of power. All this outside the actual size of the weapon itself.

All this, when the 120mm gun in the Leopard 2 and M1A2 can fire the 8.35kg DM53 kinetic energy projectile at 1750 m/s. That's 25MJ of kinetic energy.

:) I know. The actual power was 0.55MW, so about half a megawatt. That's 737HP, about 740HP. These are all educated guesstimate numbers, so I didn't think the 10% would be a huge issue.

Even if you siphoned off half the power from the turbine to power the generator, you still need that generator. Really, I can see them being used at some point in the future, but not in the next 50 years.

Correct me if I am wrong, but wouldn't it be a mass problem not a generator problem, that due to the (relatively) low mass of the tank isn't it impossible for it to project at 33MJ without being pushed backwards such that the actual impact force is offset by this amount of propulsion in the opposite direction?

If we consider this simple a conservation of momemtum problem (energy is coming from the application of electrical force), a typical M1 tank would have an end velocity of ~.2 m/s to give 33 MJ of energy to a 1 kg projectile. M1 tanks are already capable of firing amunition with 10s of MJ of energy at muzzle

you are missing the point here. The main benefit of rail guns is that they are point and shoot and never miss. The theoretical maximum is closer to speed of light than speed of sound. Rail guns would make excellent AA defense weapons and put the battle ships back on the map. They are the next best thing before lasers actually make it to weapon systems. Neither is suitable for bomber or artillery replacements and not particularly useful attack weapons due to the low rate of fire.

still, his point is valid as projectiles flying any faster - in the case of antiaircraft weapons - would essentially add no appreciable benefits to accuracy. A TI-85 adds no benefit over a free basic calculator when all you're doing is 3rd grade addition and subtraction problems.

Research into pulsed alternators at UT-CEM can be traced back to the late 1970â€™s with the invention of the compulsator (compensated pulsed alternator), a new type of low impedance electrical machine designed for very high power operation. Although it was conceived at UT-CEM to power laser flash lamps for fusion research at Lawrence Livermore National Laboratories (LLNL), the compulsator concept has been successfully applied to electric launchers for the U.S. Army and NASA, and high frequency microwave sources. Iron-core prototypes built for LLNL in the early 1980â€™s proved the operating principles of the concept. This involves the use of a compensating shield or winding in the alternator to lower its internal impedance to a very low value, while simultaneously tailoring the very large (multi-mega amp) current pulse to suit the required loads.

Iron-Core Compulsator

In the mid-1980â€™s, the first compulsator built for the U.S. Army electric gun program was successfully demonstrated. Named the "Iron-Core Compulsator" (ICC), the device is a 6-pole, rotating field machine which stores 40 MJ of kinetic energy at 4,800 rpm, and can repetitively deliver ten 1 MJ, 2 ms pulses. The ICC generates an open circuit voltage of 2 kV and operates at a peak current of 1 MA, resulting in a peak power rating of 2 GW. After fulfilling its stated contract goals by firing a burst of railgun shots at 10 Hz, the ICC has become a reliable CEM laboratory power supply for testing other components including high power switching for newer compulsators, and advanced railgun barrels.

Small Caliber

After seeing the proof of principle demonstration by the ICC, the U.S. Army then pursued the development of more compact, lighter weight pulsed power generators beginning in 1988. UT-CEM proposed and was contracted to build two single phase, self-excited, air-core compulsators. The air-core nature of the new machine concepts allowed required use of very high strength composites for construction of the rotor, which enabled it to be spun much faster - both storing more energy and making it much lighter. The first of these machines was built during the Small Caliber Rapid-Fire Railgun Program. The compulsator for this system is a 2-pole, rotating armature topology. While rated at half the power of the ICC, the small caliber compulsator weighed only 8% as much - so the power density was improved by a factor of six. The new machine demonstrated the viability of the SEAC concept and developed several new components; including the high speed composite rotor, the SCR based output switch and field rectifier.

9 MJ Range Gun

On a larger scale, the U.S. Army desired the capability to fire a large bore railgun at a test range and demonstrate the pulsed power supply at full scale. UT-CEM therefore began working on the 9 MJ range gun in 1988. Designed to launch 2 to 4 kg packages at velocities up to 4 km/s, the range gun system uses a much larger version of the small caliber compulsator as the pulsed power supply. Design features of this machine include 230 MJ stored energy, 6 kV and 3 MA peak output ratings, and 9 shot repetitive fire capability. Unfortunately, funding constraints combined with revised electric gun program focus has meant that the machine was shelved at 95% complete level.

Cannon Caliber Electromagnetic Launcher

The early 1990â€™s brought continued interest from the U.S. Army, but also from the Marine Corps. The Cannon Caliber Electromagnetic Gun System (CCEMG) is a joint project which seeks to demonstrate an EM gun system designed from a system/mission prospective. Presently undergoing lab testing, the CCEMG uses a second generation single-phase air-core compulsator which represents a factor of 3 increase in energy (3.5 J/g multi-shot) and power density (to 1,500 kW/kg) over the range gun system. The machine powers a rectangular bore railgun to accelerate 185 g launch packages to muzzle velocities far exceeding the conventional state of the art for this caliber. Rated at 4 kV and 850 kA, the compulsator stores 40 MJ and can deliver 15 shots without recharging the rotor.

Focused Technology Program

Presently, the U.S. Army is funding the Focused Technology Program to develop the next generation of compact compulsator power supplies, which will be consistent with their concept of the Future Main Battle Tank (FMBT) to be fielded by 2015 . The FTP machine concept represents a fundamental departure from the previous air-core compulsators by evolving to a rotating field topology and a multi-phase operating modes. These changes, combined with light weight composite stator structures will result in great increases in specific performance over the CCEMG machine, and will ultimately allow integration of the system into a tank vehicle chassis. The compulsator will be a part of the all-electric tank which includes electric vehicle drive and suspension, and electric armaments. In this concept, the flywheel energy can be used as a flywheel battery to provide power for vehicle acceleration and regenerative braking, and will also produce electrical power for the electromagnetic armaments.

A tank wouldn't need this amount of power. A smaller gun would suffice. Even if it were 25% less, that would be significant. And if we do see this in tanks, it will likely be a new design that was done for this purpose. I'm pretty sure the Abrams isn't the last tank design we'll have. In fact, I'm pretty sure they've got newer designs they've been working on for years.

I think this will probably be relegated to warships for quite some time until they:a) can create a compact high-density energy source to constantly charge the capacitors for this beastb) increase the efficiency significantly so they can compact the coils. I seem to recall a few articles indicating that railguns are extremely inefficient.

I don't think efficiency has anything to do with why these aren't on tanks (which are relatively small). Rather, a long rail is needed to spread out the acceleration over a longer period of time. The shorter the rail, the more the thing just acts like an explosive accelerating the projectile very quickly. Railguns aren't magic, they still do the equal/opposite reaction thing just like all other weapons that accelerate projectiles. Maybe you could put a shorter rail on a tank that's a lot less capable. (Or else maybe you don't mind that your tank goes tumbling backwards violently whenever it fires if it had a shorter rail that still transfered the same amount of energy).

quote: I don't think efficiency has anything to do with why these aren't on tanks (which are relatively small). Rather, a long rail is needed to spread out the acceleration over a longer period of time. The shorter the rail, the more the thing just acts like an explosive accelerating the projectile very quickly.

quote: Railguns aren't magic, they still do the equal/opposite reaction thing just like all other weapons that accelerate projectiles

Compared to chemically fired rounds, yes they are magic. Chemical propellant operates by generating high pressure between the back of the gun bore and the round. The high pressure pushes the round forward. But here's the catch - as the round moves forward down the barrel, the volume of space between the round and the back of the firing chamber increases, rapidly decreasing the pressure. So the round only gets maximum acceleration when first fired. After that, acceleration is constantly decreasing. (Some of Bull's cannons mitigated this problem by injecting high pressure gas further down the barrel after the round had passed.)

A railgun doesn't suffer from this. It can continue to apply full acceleration energy to the round right up until it leaves the rail.

quote: Compared to chemically fired rounds, yes they are magic. Chemical propellant operates by generating high pressure between the back of the gun bore and the round. The high pressure pushes the round forward. But here's the catch - as the round moves forward down the barrel, the volume of space between the round and the back of the firing chamber increases, rapidly decreasing the pressure. So the round only gets maximum acceleration when first fired. After that, acceleration is constantly decreasing. (Some of Bull's cannons mitigated this problem by injecting high pressure gas further down the barrel after the round had passed.) A railgun doesn't suffer from this. It can continue to apply full acceleration energy to the round right up until it leaves the rail.

This is incorrect, actually. Since WWII at the very least, they've been able to design the grains of propellant to either lose surface area as they burn, gain it, or have it remain roughly the same. The second compensates for the increased volume by burning progressively more powder, so a powder burn that isn't instantaneous (your mistaken assumption) and has powder grains increasing in size as the projectile goes down the barrel ends up able to keep the pressure relatively constant when properly designed. This was in WWII warships, tanks now definitely have it.

I think another point that most people aren't getting is railguns don't arc a whole lot since they depend on high velocity and kinetic energy. So ballistically (hehe), if you're trying to hit a target on the horizon, over a mountain, or generally not in your line of sight, it isn't going to happen.

Scaling down from 10m to 3m would reduce the muzzle velocity by 70% and power by 90%. Woefully inadequate compared to today's tank guns. To compensate you would have to increase acceleration by 3 times which requires 10 times more power transferred to the projectile over the 3m length as you used for the 10m barrel for the gun to achieve the same muzzle velocity. So power density of the field would have to increase about 33 times and the amount of capacitance needed increase ten times and also have to be able to expel the full charge three times faster. Not so easy you see?

The whole point of the project is to put these things on ships and tanks. If you flip through the PDF someone else posted, you'll see that there's collaboration on this with the Army for use in tanks. I agree we're not going to see this particular research railgun on a tank (or a ship for that matter). I was referring to whatever railgun this research eventually produces.

And wouldn't the energy transferred be reduced by 70% with a corresponding 90% reduction in muzzle velocity?

quote: Compared to chemically fired rounds, yes they are magic. Chemical propellant operates by generating high pressure between the back of the gun bore and the round. The high pressure pushes the round forward. But here's the catch - as the round moves forward down the barrel, the volume of space between the round and the back of the firing chamber increases, rapidly decreasing the pressure. So the round only gets maximum acceleration when first fired. After that, acceleration is constantly decreasing. (Some of Bull's cannons mitigated this problem by injecting high pressure gas further down the barrel after the round had passed.) A railgun doesn't suffer from this. It can continue to apply full acceleration energy to the round right up until it leaves the rail.

The bullets fired by regular guns also continue to accelerate up to the point where they leave the barrel. When you load bullets for a particular gun, you choose a certain type of gunpowder for the application. They make pistol powder burn faster than rifle powder for that very reason.

This. The shorter the barrel, the higher the acceleration over a shorter period of time (for the same muzzle velocity). Perhaps a railgun would allow for more evenly spreading out the force over the time that the projectile is being accelerated, but in the end, for every action there's an equal and opposite reaction. Again, there's no magic here. I stick by my point that muzzle velocity will have to drop significantly to put this thing on shorter rail, and to attach it to a "lighter" vehicle.

Maybe the way they intend to use it on tanks is to significantly reduce the size of the projectiles. If you get a "bullet" moving fast enough, it doesn't have to be very big at all to pass through a tank, neutralizing the crew inside. So the warship hurls huge projectiles that can travel vast distances and level buildings and the tanks spit out tiny projectiles so fast they pass through any armor. I'd buy that.

Need to read the part in the article about how right now these have a tendency to melt the rails when trying to hit such high velocities. If you shorten the rail, you will also increase the temperatures which are produced by the greater acceleration needed to gain the same speeds in the shorter distance. I can't imagine needing to replace the rails after a shot or two in a tank, that would not be very efficient.

It also says that without huge capacitor stacks on a warship the warship generator would not be able to fire more than a round or two per minute, the power available in a tank format would make firing even slower, also not good for a ground battle situation.

quote: Last I heard of this technology I dont believe they shoot explosive rounds but round circular tubes that the velocity alone destroys the target. Potentially on the plus side we dont have unexploded munitions lying around.

You do know the standard AT round is HVAPFSDS, or in layman, a high velocity fin stabilized dart that uses kinetic energy alone to destroy the target? Any tank with a smoothbore is basically designed only for kinetic energy round, HE rounds need volume and that doesn't fit with fin stabilization which generally needs a sabot to work properly.

How useful would this sort of weapon be on a tank? Assuming that you could power it, as discussed in the multitude of comments above.

Would the range of the weapon, tank to tank, be limited to line of site and the curvature of the Earth, as the projectiles travel at such high speeds as to make them behave in the same sort of way as a laser?

Do current tanks have a range that relies on a parabolic type trajectory, where the shell is "lobbed" and as such can actually hit targets on the ground further away than a rail gun projectile could.

quote: Do current tanks have a range that relies on a parabolic type trajectory, where the shell is "lobbed" and as such can actually hit targets on the ground further away than a rail gun projectile could.

I would think if you needed to "lob" the projectile over some sort of terrain, you could simply reduce the power of the railgun to achieve the same, slower muzzle velocity. I would imagine an onboard computer could pretty easily calculate the angle and power that would deliver the most energy to the target.

quote: ...you could simply reduce the power of the railgun to achieve the same, slower muzzle velocity

Wouldn't that entirely defeat the object of a rail gun, which are about delivering energy to the target through a ludicrously fast projectile?

I wasn't really talking about over some sort of terrain either. My English was perhaps a little, how you say, inelegant.

Basically, doesn't the parabolic trajectory of conventional cannons allows artillery and tanks to fire "over" the horizon? Wouldn't a rail gun fire, quite literally, over the horizon, and on and on and on?

By the way, I get what you mean about reducing the speed of the projectile as an option, whilst firing at silly high "conventional" rail gun speeds when a line of sight is available. However, you will need to use some sort of explosive round to have any affect on the target at the lower speed, which I'm not sure is the plan.

Tanks are armored artillery. Within the limits of their gun travel and range, they can fire over hills or over the horizon at targets that are out of line of sight.

All they need are accurate targeting coordinate to aim the gun with.

The most common usage is line of sight, but for all but point blank shots, the shell rises on the way to target, then drops. When range, trajectory and velocity are all set correctly, the shell passes through the target as it follows it's normal trajectory.

To fire over a hill, you aim high and fire with a relatively low velocity ... similar to pitching at a batter vs throwing a ball over a house to a catcher on the other side.

quote: Yeah, now I'm left wondering when or if this technology can be used to create a gun to send/shoot something fast enough across the galaxy in a reasonable amount of time (like a mass relay station!).

Doubtful. It might work as a launch vehicle (for cargo) - it's a toss-up whether railguns or gas guns will turn out to be more practical for that application. As a launch vehicle, you're not launching your fuel with the payload, which can mean a 95%-99% weight savings, which is just huge. (A gas gun works by using a light gas like hydrogen whose compressed and heated molecular velocity, and hence the highest speed it can accelerate something, is greater than escape velocity.)

For use in space travel, they just don't generate enough velocity. This gun can currently fire a payload at 3000-5000 mph. Escape velocity from Earth is 11.2 km/s, or 25,000 mph. Due to kinetic energy being the square of velocity, it costs you a lot more energy to increase payload velocity from 24,000 to 25,000 mph than to increase it from 4000 to 5000 mph. You are better off carrying your fuel with you and using a rocket or railgun to fire the fuel backwards, using the momentum balance to increase your velocity further. (In kinetic energy terms, it costs less energy to fire your propellant backwards than your spacecraft forward because your propellant, even though it's fired backwards relative to your spacecraft, is still moving in the same direction as your spacecraft from the reference frame of where you'd be launching the spacecraft - the Earth.)

As it turns out, a "railgun" for firing propellant at high velocities out the back of your spacecraft has already been invented. It's called an ion thruster, and can fire xenon atoms at about 28 km/sec, or 60,000 mph.

Well not this specific one, but I did build a rail gun in High school about 12 years ago. It shot a steel ball bearing a few feet.I had hoped it would go further, but the prof was quite impressed it worked at all. Apparently a few other people tried to make one over the years but it never did much.

I made the magnets myself, coiling wire around some iron spikes. Control method was pretty simple, V-shaped rail with one side being solid, the other having cuts in it to control when each magnet fired. No fancy computer control, but it worked. I'd love to rebuild that one day.

Sound to me you were building a coil gun. The difference between coil gun and rail gun is that coil gun uses magnetic energy to accelerate the projectile where rail gun use the electric field. Coil gun is what people often think when talking about rail guns. The reason I think you were building coil gun is that rail guns usually turn their projectiles into plasma.

The aerodynamic shape of the projectile is not a big concern because it's going to be flow formed by the drag into a shape of drop anyway. This is also cause of the rail meltdowns.

This new railgun fires rounds with an energy of 33 megajoules. It sounds like a lot, but it's not really that much for a weapon of that size. For comparison purposes:

The USS Monitor from the Civil War had a gun with 6 Megajoules.The Iowa class battleships from WWII fired with an energy of 350 Megajoules. The British had a battleship gun in 1915 that was 410 Megajoules.

So in other words, this isn't really going to give you any new capability that we didn't have over 100 years ago.

Well in the area of cost/damage analysis this could allow you to wreck a smaller target with better accuracy and minimal collateral damage all while saving the tax payers money. Hey now that's an idea.

quote: Well in the area of cost/damage analysis this could allow you to wreck a smaller target with better accuracy and minimal collateral damage all while saving the tax payers money. Hey now that's an idea.

1. There's no reason that a conventional artillery gun can't be accurate. I'm willing to bet that you could make an artillery shell more accurate than a railgun projectile since you could make a guided artillery shell. So far, there are no guided railgun projectiles.

2. With a solid armor piercing shell instead of a high explosive shell, you wouldn't have a lot of collateral damage. You'd be dealing with kinetic energy from the shell.

3. I'm willing to bet that the cost of designing, building, and operating a railgun is much, much higher than purchasing steel and gunpowder.

Basically, at this point the rail gun is not practical. It's shown possibility but missiles and shells can do the job more effectively.

Except the point the Navy is making about railguns is the ability to deliver the weapon over hundreds of miles at high velocity for the cost of a bullet (comparatively). We have weapons that can travel hundreds of miles (cruise missiles, aircraft; but expensive), and we have weapons that can deliver quickly (artillery; but limited range). A railgun combines the best of both worlds. Since bombs and missiles with their (relatively) low speed need explosives to ensure a probability of kill, a solid shot will reduce overpressures and fragmentation issues with containing collateral damage.

As for steel and gunpowder doing this cheaper, I'm not sure that that's feasible, considering Bull's supergun and others like it haven't been exactly winning awards, mostly because the size alone of the systems makes it impractical for anything other than a fixed launch site. The costs associated with having to tear down/build up such a system everytime you needed to significantly change direction, or build a turntable system large enough to hold it would be large indeed.

Maritime navigation uses nautical miles because a nautical mile is equal to one minute of latitude, or one minute of longitude at the equator (1/60th of a degree). It's somewhat arbitrary, but it makes it a helluva lot easier to eyeball distances on a chart which is labeled in degrees latitude/longitude.

That and he's reporting Navy news, and the Navy uses those units for that very reason, so any comparable figures you'll find are almost certainly in knots as well. Much better to leave it in nmi like the rest of the comparable weapons systems so you can compare it more easily.

For those playing at home, the unit of energy in imperial units is called a ft-lb force (lb plays the double role of force and mass). Though the hp*hr is probably better. In this case, this thing is a 12.2 hp*hr railgun. Ah, that's sounding impressive enough guys, can't we convert to Joules?

That description brings to mind the MAC (Mass Accelerator Cannon) of human ships in the Halo lore. Basically a massive railgun (or 3) mounted down the spine of the ships. It would be an interesting design... just make sure your target can't outrun your rate of turn.

Anybody wonder about the projectile used? The (simply marvelous) hi-speed video of the shot shows a relatively square object, with tail strakes. [Which is what actually got ME to thinking about Mass Effect].

Now, you'd think, if I were shooting something at Mach 8 I'd make it somewhat aerodynamic. At the very least, the projectile would have a lifting-body design. No?

I have no idea what I'm talking about here, but a couple of ideas may be that the shape is so that it responds to the magnetic field in the railgun most efficiently, or maybe it's so that the projectile will create the most damage, rather than simply piercing its target.

Not quite a megajoule was my initial gut reaction. A quick, back of the envelope calculation confirmed your number (approximately 0.906476 MJ).

Now if the author had completed the units missmatch and gone with a "metric ton" of approximately 2,204.6 U.S. pounds then he'd have had 0.999 MJ wich is close enough for most people to call a megajoule.

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